Two-part acrylate formulations are well known in the art for use as adhesives, potting compounds, conformal coatings, and the like. In addition to including polymerizable acrylate monomers, such formulations typically include elastomeric fillers (e.g., urethane oligomers, preferably capped to provide sites of unsaturation for enhanced reactivity), adhesion promoters in the form of organic acids (e.g., acrylic and methacrylic), inert fillers, supplemental adhesion promoters (e.g.) silanes), leveling agents, and other ingredients. Reaction in formulations of this kind is normally initiated by use of a free-radical, active-oxygen catalyst (i.e., a peroxide, a hydroperoxide, or a perester), activated thermally, chemically (e.g., with an amine/aldehyde adduct and transition metal accelerator), aerobically, anaerobically, etc; they may additionally or alternatively include a photoinitiator that is responsive to actinic radiation.
Illustrative of the prior art that is germane to the acrylate formulations hereinabove referred to are the following Bachmann and Bachmann et al United States patents, all of which are of common assignment herewith: U.S. Pat. Nos. 4,348,503, issued Sep. 7, 1982; 4,429,088, issued Jan. 31, 1984; 4,432,829, issued Feb. 21, 1984; 4,963,220, issued Oct. 16, 1990; 4,974,938, issued Oct. 23, 1990; and 5,039,715, issued Aug. 13, 1991.
Other prior art of interest to the subject matter to which the instant application pertains are the following, each of which is also a patent of the United States: Lappala, U.S. Pat. No. 2,859,200, issued Nov. 4, 1958, DiMartino U.S. Pat. No. 2,921,045, issued Jan. 12, 1960, Lees U.S. Pat. No. 3,658,624, issued Apr. 25, 1972, Skoultchi U.S. Pat. No. 4,052,244, issued Oct. 4, 1977, Wolinski et al U.S. Pat. No. 4,126,504, issued Nov. 21, 1978, Nativi U.S. Pat. No. 4,424,252, issued Jan. 3, 1984, Kubota et al U.S. Pat. No. 4,820,744, issued Apr. 11, 1989, Gutek U.S. Pat. No. 4,956,221, issued Sep. 11, 1990, and Chao Registration No. H509, published Aug. 2, 1988.
The Lappala and DiMartino patents disclose the combined use of a number of ingredients for the catalysis of acrylate systems; for example, DiMartino describes a methylmethacrylate cement that includes methacrylic acid and is catalyzed by cobalt naphthenate, MEK peroxide, and diethylaniline, used in combination. The Lees patent lists complimentary accelerators, including a monocyclic carbocyclic aromatic acid (e.g., benzoic), trichloroacetic acid, and phenoxyacetic acid. The two-part adhesive disclosed by Skoultchi includes p-toluene sulfinic acid, and Wolinski et al disclose a system that includes an acid (e.g., acrylic) and a free-radical, active-oxygen catalyst (e.g., benzoyl peroxide), in which reaction is initiated by a tertiary amine (e.g., dimethyl-p-toluidine). Both Nativi and Gutek provide compositions that afford shadow curing capability, and Gutek discloses UV-curing as being suitable for printed circuit board applications.
Despite the activity in the art indicated by the foregoing, a demand exists for a highly effective two-part formulation comprised of polymerizable, oxygen-containing ethylenically unsaturated (e.g., acrylate) monomers, which is suitable for use as an adhesive, for potting, for conformal coating, and for other like applications, which formulation does not depend upon a free-radical, active-oxygen catalyst for initiation of reaction. Accordingly, it is a broad object of the present invention to provide a novel formulation having such features and advantages.
A related object of the invention is to provide such a formulation from which highly satisfactory cured deposits can be produced despite the lack of intimate admixture of the two components of which it is comprised.
A corresponding object of the invention is to provide a novel catalyst system for use in such formulations.
Another corresponding object is to provide a novel method for the production of an adherent, solid deposit in a highly facile and yet efficient manner, utilizing a two-part formulation of the character described.